Digester



2 Sheets Sheet 1. S. SMITH. DIGBSTER.

P atented'Dec. 30, 1890.

(No Model.)

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(No Model.) 2 SheetS-Sheet 2.

s. SMITH.

DIGBSTER.

No. 443,924. Patented Dec. 30, 1890.

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Nrrn Sterns A Priene y SIDEY SMlTll, OF CAMBRIDGE, MASSACHUSETTS.

DIGESTER.

SPECIFICATION forming part of Letters Patent No. 443,924, dated December 33, 1890. Application i'iled Jnne 29, 1889. Serial No. 316,060. (No model.)

.To all whom, it may concern:

Be it known that I, SIDNEY SMITH, of Cainbridge, in the county of Middlesex and State of Massachusetts, have invented certain new and useful Improvements in Digesters, of which the following is a specification.

This invention relates to a digester having an inner coating composed of sulphite of lime or otherchemical salt precipitated and fixed uniformly on all parts of its inner surface that are exposed to the liquid contents, said `coatingl being produced by the direct impingement or action of the heated products of combustion of any suitable fuel upon the outer surface of the metal of the digester and the contact at the same time of a suitable solution with the inner surface of the digester, the result being the deposit-ion of a chemical salt or incrustation, which protects the metal from injury during the subsequent operation of cooking` wood chips in an acid liquor.

The object of the invention is to produce" a pulp digester which may be maintained at a uniform temperature and may be readily controllable, whereby the digester is lined or coated with a chemical incrustation, the constituents of said interior coating being derived from the liquor used in digesting the pulp or being such constituents as are einployed in such digesting` fluid.

The invention consists, further, of an arrangement of dampers and lines surrounding the digester, so arranged that the temperature and pressure within the digester can be raised, perfectly controlled, and maintained. The arrangement of fines and damper-s also makes possible a rapid cooling` down of the surroundingflues, which is desirable previous to the expulsion of the contents of the digester, by blowing off under any desired press- Openings covered by mica are out through the surrounding brick-work into the flues at suitable points for observing the action of the hot gases and for the insertion of any convenient device for determining the temperature in theflues. The fire-box stands in connection with the chimney by means of a direct flue, and also by means of the series of indirect flues surrounding the digester, so that by use of dampers the products of combustion may be taken directly to the chimney without touching the digester, or may be allowed to stream up and around the digester, passing finally to the chimney. As shown in the drawings, the walls of the finalor down flue are so curved as to deflect the hot gases and air and compel lthem to travel close to the digester-shell. At the front of the firebox openings covered by doors are placed in the brick-Work, so that cold air may be drawn in on a level with and directly over the highlyheated fuel. This air is not intended for increasing the combustion, but is rather intended to check the increase, but at the same time to better utilize the heat already produced by carrying it forward to the flues around the digester and diffusing it in a uniform manner. The fire is thus prevented from becoming too intense, and the accelerated circulation prevents injurious concentration of the heat upon the nearest por- Ktions ot' the digester-shell and tends to the production of a nearly uniform temperature throughout the iiues. An opening is provided for the admission of cold air to the flues extending along the digester, so that byopening a door covering said opening the walls of the casing surrounding the digester may be rapidly cooled down to prevent injury to the digester by the radiation of heat from said walls upon the digester after the contents of the latter have been blown olf or otherwise re- In the accompanying drawings, forming a part of this specilication,Figure l represents a side elevation of a digester and a vertical section of the casing inclosing the same and of the fire-box and tlues. Fig. 2 represents a section on line a: 0c, Fig. l. Fig. 3 represents a section on line y y, Fig. l. Fig. et represents a section on line z z, Fig. l.

The same letters and figures of reference indicate the same parts in all of the gures.

In the drawings, a represents the digester, which is constructed of boiler-iron or steel or other suitable material, and is inclosed in the casing or setting l) of masonry, said casing being separated from the digester by a space which surrounds the digester, excepting at the top, where the top of the casing is brought into the Walls of the digester. Said space is partially divided by two vertical partitions c c, which extend vertically from thc base or foundation portion of the casing IOO nearly, but not entirely, to the top of thecasing, and convert the space surrounding the digester into two flues e f, the former being called the upward and the latter the downward Hue. Each partition c is composed of a Vertical brick wall 9, extending inwardly from the inner wall of the casing or setting partly, but not entirely, across the space between'said wall and the digester, and a flexible sheet 10, of asbestus board, set edgewise in said wall and extending across the remaining portion of said space, its outer edges being free to bend or move and bearing yieldingly against the periphery of the digester. This construction permits the digester to expand and contract freely without injuring the setting by its expansion and without forming streaks between its periphery and the partitions c by its contraction.

g represents the furnace or fire-box, which is located at the lower end of the upward flue e, but not directly under the same, as shown in Fig. 1, and communicates with the flue c through an opening h over the bridge-wall i. One side of said opening is curved, as shown at 7L', said curve connecting the arched top of the fire-box with the vertical outer side of the flue e and forming not only an enlargement of the opening 7L, but also a surface which guides the heated products of combustion so that they do not impinge directlyon the bottom of the digester, as would be the case if the top of the fire-box joined the outer wall of the flue c at a right angle, said products of combustion being caused to assume a yertical direction by the curved surface h rather than by impingement against the surface ot' the digester. Overheating of the digester at the portion nearest thcopening 7L is thus prevented.

In the walls of the tire-box are openings for the admission of cold air, arranged as near the level of the lire as possible, so that cold air may be admitted to the top of the fire and be there mingled with the heated products of combustion. The air thus admitted docs not promote combnstion,but carries the heat forward through the tlues ef, diffusesit uniformly, and prevents an excess of heat. Said openings may be made especially for this purpose, as shown at r,Fig. l; orthe redoor may have a lowersection j, whichis connected to the main portion ot' the door by horizontal hinges, so that it can be opened by swinging it upwardly, thus forming an opening for the admission of air close to the level of the tire.

t'represents a series of passages arranged to conduct air through the heated bridge-wall and deliver the same to the tire-box.

m represents a slide or damper, which is arranged to close the opening 7L when itis desired to shut oft' the heat from the tlues e f.

- lVhen said slide or damper is closed, the heat passes through the flue a at the bottom of the casing to thc direct Aflue or stack 0 without contact with the di gester.

p represents an opening in the casing for the admission of cold air to the lower portion of the flue e, so that whenit is desired to rapidly cool the walls surrounding the digester a door g in said opening may be opened and cold air admitted to the lines e f. The object of thus cooling the walls is to prevent injury to the digester by radiation of heat from said walls when the contents of the digester have been blown out. It is necessary to quickly discharge thc contents of the digester when the cooking has reached a certain stage, and if the walls are not quickly cooled serious injury to the digester will result from the radiation of heat from the walls. The openingp affords suitable means for the rapidly cooling of the walls. The lower portion of the fluef communicates with the direct flue or stack 0 by a passage f', through which the products of combustion passto the stack. The wall of this downflue is curved to detlect the hot gases and air against the lower curved end of the digester-shell.

In the upper portion of the direct tlue o is a slide or damper r, which, when opened, is moved outwardly or away from the Wall s, that separates the Iiue o from the uef. The object of said damper is mainly to contract the iiue o and cause the heat to impinge against the wall s in its upward passage, the damper closing toward said wall,so that the products of combustion in escaping have to pass between the damper and wall. The escaping heat is therefore partially utilized by heating the wall s, and thus maintaining a higher temperature in the flue f.

w represents a sight-opening formed in the casing b to permit the inspection of the tlues, so that the conditions therein existing may be readily determined. Said opening is covered with a sheet u, of mica or other suitable transparent material. There may be any desired number of these openings, and they may be located at any desired points.

2 represents a' blow-off pipe, which extends from the lower portion of the digester to permit the discharge of the contents thereof.

3 represents a vertical pipe within the digester for the circulation of the liquor therein. Said pipe has two arms 4 4, attached to and extending horizontally from its upper end and bearing at their outer ends on a shoulder 5 on the digcsters. The object of said arms is to support the pipe 3 and keep it at the center ofthe digester, and this is accomplished by the bearing of said arms on the shoulder 5. The arms are preferably made of lead to resist the action of the chemicals.

The formation of the coating is not contin ed to any one liquor, nor is it necessary that the liquor used for the purpose of producing the coating should at the same time be adapted for cooking the wood or iibrous material,

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for the digester may be rst lined by means of appropriate liquor, and then used with any other liquor suitable to act upon the wood without at the same time injuring the coating previously formed.

The digester may be made of any metal or material capable of withstanding the tcmperature and pressure employed in the process.

An essen tial feature of the invention is the direct impingement or action upon the outside of the material forming the digester of the heated products of combustion of any suitable fuel, whereby the presence on the inner side of said material of any solution capable of yielding` a deposition forms a coating for the interior of the digesterin the application of heat, said deposition being fixed at the same time and by heat. While it may be the most convenient and practicable way to fill the digester when in position for use with a suitable liquor and then apply heat externally to produce an inner coating, the underlying principle involved is not that of fusion of certain ingredients and baking upon the shell, asin the case of an enamel, but is the chemical deposition of the salt or substance forming the coating by decomposition or concentration, accomplished by heat in the manner described.

A good process of providing the interior of the digester-shell with a protecting-coating is as follows: The digester, which is set in a casing of brick-work and heated by the products of combustion passing through the ascending and descending` tlues, is first filled with wood chips about to the point where the conical lead-lined neck is attached to the digester. .Acid liquor, which is designed to act upon the gums, resins, &c., of the wood, is now admitted to the digester. lllhile the liquor is running in the digester is gentlyheated by allowing the heat from a low fire to pass through the flues. An observer looking down into the digester from the top will note that the White coating has already begun to form where the liquor has come in contact with the already-heated shell of the digester. No definite temperature need be adhered to. It is only necessary to keep the temperature low enough not to injure the digester-shell or send forth sulphurous-acid gas in amounts large enough to seriously inconvenience the workmen engaged in filling the digester. W'hen the liquor has reached the junction of the lead lining with the steel shell, the cover is securely bolted on and the fire is urged. If the formation of the coating were the only obj ect at stake, the digester might be strongly iired from this point on; but as a uniform and complete cooking` of the wood is an important element in the process it is the practice to slowlybring the pressure and temperature within the digester up to the maximum desired only after the lapse of some four or five hours. These maximum conditionsof temperature and pressure are then maintained as carefully as possible until the operator is assured that the wood chips are completely freed from the incrusting gums, &c.

The total time of cooking from the time the man-hole plate is bolted on to the time when the cooked pulp is blown out from the pipe at the bottom is avariable one, but may be from fifteen to twenty hours. When thc contents have been blown out at the end of the cooking process, that part of the interior which has been in contact with the liquor Will be found coated with a thin, firm, uniform incrustation. If bisulphite of magnesium were the liquor used, the incrustation Will consist of a White coating of monosulphite of calcium or of monosulphite of magnesium. Both the steel of the shell and the lead lining of the neck will be coated to the height covered by the liquor during the whole time of cooking. There is no coating where the liquor has not been in contact with a metallic surface, and for this very reason the neck and inner side of the man-hole cover are lined with lead to protect the iron beneath from the action of the sulphurous-acid gas which is expelled from the liquor by heat and collee-ts above the level of the liquor in the expansion-chamber formed by the neck. The monosulphite of calcium adheres wherever it comes in contact with a metallic surface which is heated from the opposite side. Some of the monosulphite of calcium is deposited upon the pulp and must be subsequently 'washed out before the pulp is made into paper.

Heretofore sulphite-digesters have generally been heated by free steam or a steamcoil on the inside or by a steam-jacket on the outside, while in this case the source of heat is the combustion of any suitable fuel outside the shell of the digester and in direct communication with the said shell, so that the products of combustion act directly thereon. 'lherein lies the marked difference in method and the cause for a marked difference in results, for the incrustation can be perfectly formed only when the shell is heated by the direct impingement or action of the heated products of combustion of a suitable fuel on the digester with the properliquor in contact with the plate.

rlhe process herein described of forming a protecting inner coating for the digester as well as the coating itself does not form part of the subject-matter of the claims in this case, since the above are embraced by my pending application for patent, liled March 77 1889, Serial No. 302,277.

I claiml. The herein-described improved apparatus for producing pulp, comprising the digester, the furnace or fire-box, a casing inclosing the digester, upward and downward flues surrounding said digester, and a stack or chimney outside of said casing, said upward iiue extending upwardly from and communicating with the rear portion of said I'ire- IIO IZO

box, and the lower end of said downward flue connecting or communicating directly with said stack or chimney, substantially as and for the purposes set forth.

2. The combination, with a digester, of a furnace or fire-box, a casing inclosing the digester and subdivided to form upward and downward flues extending along the diges'ter, said upward ue extending upwardly from and communicating with the rear portion of the tire-box, and openings through the walls of the tire-box above the tire therein for the admixture of cold air with the heated products of combustion immediately above the fire, as set forth.

3. In an apparatus for producing wood pulp from chips of wood under the action of bisulphite liquor or other chemical salt and forming a continuous inner protecting-coating on the digester, the combination of the digester, a casing therefor having upward and downward llues throughout thelength of said digester, and a firebox or furnace located at and to one side of the bottom of said upward flue and opening thereinto and provided with cold-air-supply openings, and having its arch or top curved or deflected upwardly to join the vertical wall of said flue at said opening, whereby the products of combustion are prevented from impinging directly on the bot-v tom of the digester and a nearly uniform temperature is secured, substantially as set forth.

4. The combination of a digester, a casing therefor having upward and downward ilues, a fire-box or furnace located at the bottom of the upward liuc, a direct Hue or stack located beside the downward flue and communicating with the lower end thereof, and a damper in said direct flue, whereby the heated products of combustion may be caused to impinge against the wall which separates the downward llue from the direct liuc, as set forth.

5. The combination of a digester, a casing therefor having upward and downward fines, a lire-box orfurnace communicating with the lower port-ion of said upward flue, and an opening for the admission of cold air into the lower portion of the upward flue, as set forth.

6. The combination of the digester having an internal shoulder 5 at its upper portion, and the circulating-pipe 3, having the arms 4 bearing on said shoulder, whereby the pipe is removably supported above the lower end of the digester, as set forth.

7. The combination, substantially as hereinbefore set forth, of a sulphitedigester, a furnace or fire-box offset or removed from the digester, a conduit communicating with the iirebox and with the exterior of the digester and adapted to conduct the products of combustion to and along or in contact with the exterior of the digester, means for controlling or shutting off the communication between said tire-box and conduit, whereby the action of the products of combustion on the digester may be controlled, and a stack or chimney communicating with said furnace or irebox, as set forth.

S. The combination, substantially as hereinbefore set forth, of a sulphite-digester, a furnace or lire-box offset or removed from the digester, a stack or chimney, a conduit communieating with both the tire-box and chimney and arranged to conduct the products of combustion along or in contact with the exterior of the digester, means for controlling or shutting off the communication between said fire-box and conduit to control the action of the products of combustion on the digester, and another conduit or flue adapted to conduct the products of combustion from the fire-box directly to the chimney, avoiding the digester, as set forth.

9. The combination of a digester, a casing of masonry having vertical partitionwalls which subdivide the space between the digester and the casing into fines, and flexible sheets of asbestus incorporated into said walls and extending edgewise therefrom to the periphery of the digester, the inner edges of said sheets .being free to bend and bearing with a yielding pressure on the digester, as set forth.

In testimony whereof Iaffix my signature in presence of two witnesses.

SIDNEY SMITH.

Witnesses:

W. A. BARTLETT, PHILIP MAURO. 

